Ternary zirconium alloys



United States Patent TERNARY ZIRCONIUM ALLOYS Walston Chubb, Columbus, Ohio, assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application February 18, 1954, Serial No. 411,291

7 Claims. (Cl. 75-177) This invention deals with a zirconium-base alloy, and in particular with a zirconium-base alloy containing tin.

It is an object of this invention to provide a tin-containing zirconium alloy which has a high tensile strength at elevated temperatures.

It is another object of this invention to provide a tincontaining zirconium alloy which has a high degree of ductility.

It is finally also an object of this invention to provide a tin-containing zirconium alloy which has good corrosion resistance.

Zirconium alloys nowadays find a great many applications for elements or parts of constructional equipment that are subjected to high temperatures and/or corrosioncausing conditions such as for chemical apparatus. Many metallic additives have been found sufiiciently soluble in zirconium to form binary alloys. For instance, aluminum, lead, molybdenum, niobium, tantalum, tin, titanium and vanadium have been added to zirconium, and binary alloys have been thus produced which have some of the desirable qualities. However, these alloys mostly have insufiicient strength or too low a ductility to make them suitable for the above-outlined purposes.

It has now been found that zirconium-tin alloys which contain a relatively small amount of molybdenum have all the properties combined which make them excellently suitable for use at high temperatures and under corrosive conditions. While the contents of tin and molybdenum may vary widely, the ranges of from 0.2 to 3.5% by weight for the molybdenum and from 1.5 to 7% by weight for the tin are preferred. The best alloys are obtained by restricting the tin content to between 1.8 and 4.5% and the molybdenum content to between 0.4 and 3.3%.

The alloys may be prepared by any method known to those skilled in the art. As far as high strength and hot-hardness are concerned, arc-melting has been found to yield the best alloys. However, excellent proper-ties are also obtained by preparing the alloys by inductionmelting. All the alloys discussed in detail in this specification have been made by induction-melting.

For this purpose, a total charge of about 200 grams of metal was introduced in two portions into a non-outgassed graphite crucible; after the first half was melted the remainder was added. Melting was carried out at an absolute pressure of below microns of mercury in a high-frequency induction furnace. About 10% of the charge was usually absorbed by the graphite crucible, so that ingots weighing about 180 grams were obtained of each alloy.

A great number of alloys of various compositions were thus prepared and tested as to their hardness, hot-hardness, tensile strength, elongation, and corrosion resistance, the characteristics primarily of interest for the purposes for which alloys of this invention are to be used.

For the hardness tests the as-cast alloys were upsetforged and hot-rolled at 1000 C. to form slabs /8-iIlCh thick. These slabs were cleaned by sand-blasting and then cold-rolled to sheets of a thickness of 0.070 inch. These sheets were rather brittle, but annealing for one hour at 700 C. in a straightening press considerably increased their ductility. The annealed sheets were then cleaned by grinding up to 0.015 inch from each side and then cut into tensile specimens. The cold-hardness data were obtained during this procedure of making the alloys.

Hardness data of most of the alloys were also obtained at several elevated temperatures by means of a vacuum hot-hardness machine. This machine was designed especially for determining the hardness of metals and alloys at temperatures up to 1000 C. The machine employs dead-weight loading on a Vickers pyramid-sapphire indenter. The indentations are made by raising the specimen into contact with the indenter and by further raising the specimen until the dead-weight load is raised off a rest. The indenter and specimen are heated by resistance-heating coils which immediately surround them. The temperature of the specimen is recorded by means of a thermocouple which is in contact with the lower surface of the specimen. A screw-operated bellows is used to raise and lower the specimen. An indexing device enables the specimen to be moved laterally so that several indentations can be made on a single specimen. The machine has been operated successfully at temperatures up to 1000 C. with an absolute pressure of less than 5 microns of mercury. Scatter of individual hardness numbers obtained at a given temperature is about 10% of the mean hardness reading.

In the tests described here, five indentations were made at each temperature up to 450 C. and at least three indentations were made at each temperature above 450 C. Hardness numbers calculated from these indentations were averaged and plotted. The temperatures for the tests were selected so as to give points every 50 or C. Smooth curves were drawn through these points, and the values of interest were then read from the curves.

For determining the tensile strengths of the various alloys, specimens were cut therefrom which had a length of 5 inches, a width of 0.75 inch and a thickness of 0.06 inch; the reduced section was 1.5 inches long and 0.5 inch wide. Some zirconium-tin alloys, for comparative purposes, were also tested; these specimens had a total length of 6 inches and a 3-inch long reduced section but otherwise the same dimensions as the specimens of the ternary alloys. The specimens were taken parallel to the rolling direction. The tests were carried out at 500 C. in an argon atmosphere with the head of the testing machine traveling at 0.02 inch per minute. An extensometer with a l-inch gauge length and an accuracy of 0.0001 inch per inch was used to measure the extensions. The tests were run in duplicate and the averages were taken.

Determination of the elongation was carried out by punching bench marks in a distance of 1 inch in the tensile specimens to be tested. After testing, the two halves of the broken specimen were placed together and the distance between the bench marks was measured. The increment in distance between the marks was an indication of the elongation of the specimen.

Hardness tests were also made after heat-treatment of the alloys. For this purpose small pieces of each alloy were treated, (a) by soaking the alloy for one hour at 950 C. and then brine-quenching it, and (b) by aging the thus brine-quenched alloy for six hours at 550 C and the hardness determined after both treatments.

The alloys were furthermore tested as to their corrosion resistance and for this purpose small pieces thereof were immersed in water at 360 C. in a bomb of stainless steel. The best results were obtained with an alloy containing 3.4% by weight of tin and 0.9% of molybdenum; this alloy survived 720 hours of the corrosion test treatment.

In the following table the results are summarized which were obtained with some of the alloys tested.

Table Results 01 Tests:

Sn, Percent 1.5 1.7 1.9 1.8 3.4 4.0 4.0 4.5 2.0 4.0

Mo, Percent 1.3 1.5 0.8 3.3 0.9 0.4 1.6 1.5 0.9

0.2 percent offset yield strength at 500 0., p. s. i 28,800 20,500 21,900 42, 200 27, 800 25, 300 38,800 38,100 29, 900 13,600 25,100 6, 300 Ultimate strength at 500 C., p. s. i 36, 400 32,100 30, 900 54, 900 37,100 37, 200 53, 400 52, 500 42, 500 20, 700 34,000 11,100 Elongation in 1 inch at 500 0., percent... 32 14 33 22 26 48 27 27 42 24 67 Reduction of area at 500 C 48 9 32 34 56 44 36 40 35 56 Hardness, Rockwell A:

d, Cold-rolled and annealed 1 Soaked 1 hr., 950 C. and brine-quenched Brine-quenched from 950 C. and aged 6 hrs., 550 0.... Diamond-Pyramid Hardness Number, kg./mm., at:

(*) Was not cold-rolled because too brittle.

It is obvious from the table that the 0.2% offset yield strength of zirconium-tin alloys is remarkably increased by the addition of molybdenum. The alloy containing 1.8% tin and 3.3% of molybdenum showed the highest 0.2% ofiset yield strength, namely, of 42,200 p. s. i. at 500 C., and the next best alloy in this respect was the alloy containing 4.0% tin and 1.6% molybdenum which had a 0.2% offset yield strength of 38,800 p. s. i. Pure zirconium in comparison thereto has a 0.2% ofiset yield strength of 6300 p. s. i. at 500 C. while stainless steel 347, which is a steel containing from 17 to 19% chromium and from 9 to 12% nickel, has a yield strength of 31,000 p. s. i. at 500 C.

The ultimate strength at 500 C. was also improved by the addition of molybdenum to the zirconium-tin alloys. Here again the best results were obtained with the alloys containing 1.8% of tin and 3.3% of molybdenum and containing 4.0% of tin and 1.6% of molybdenum.

As to the elongation and reduction of area values of the ternary alloys, the alloy containing 4.0% of tin and 0.4% of molybdenum was the most satisfactory. The best cold-hardness values were found in alloys containing 4.5 of tin and 1.5% of molybdenum and with an alloy containing 3.4% of tin and 0.9% of molybdenum; the latter of the two alloys was the one which showed the highest corrosion resistance.

Alloys containing 4.5% of tin and 1.5% of molybdenum and 4.0% of tin and 1.6% of molybdenum were superior as to hot-hardness. All these data show that the addition of molybdenum to zirconium-tin alloys improves most of the properties of interest and that alloys are obtained which are very well qualified for use as construction material and chemical equipment which are to be exposed -to high temperatures and corrosive conditions.

It will be understood that this invention is not to be limited to the details given herein but that it may be modified within the scope of the appended claims.

What is claimed is:

1. A ternary zirconium-base alloy containing from 1.5 to 7% by weight of tin and from 0.2 to 3.5% of molybdenum.

2. The alloy of claim 1 wherein the tin content ranges from 1.8 to 4.5 and the molybdenum content from 0.4 to 3.3%.

3. A ternary zirconium alloy containing 1.8% by weight of tin and 3.3% of molybdenum.

4. The alloy of claim 2 containing 3.4% of tin and 0.9% of molybdenum.

5. The alloy of claim 2 containing 4.0% of tin and 0.4% of molybdenum.

6. The alloy of claim 2 containing 4.0% of tin and I References Cited in the file of this patent Anderson et al.: Bureau of Mines, Report of Investigations 4658, A Preliminary Survey of Zirconium Alloys, March 1950, pp. 30-32 and 42 and 43. 

1. A TERNARY ZIRCONIUM-BASE ALLOY CONTAINING FROM 1.5 TO 7% BY WEIGHT OF TIN AND FROM 0.2 TO 3.5% OF MOLYBDENUM. 